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Cadillac STS/STS-V: Transmission
I just purchased a 2003 Cadillac Seville STS with 28,000 miles on it. When i test drove it everything seemed to be okay, but after driving it about 200 miles I noticed that sometimes if I would accelerate fast off the line, the shift from 1st to 2nd gear would be so harsh that the tires would screech. I thought that maybe the transmission fluid was low, so I checked it and it was up to the right level and it wasn't a nice pink color. I went to pep boys and got a bottle of Lucus transmission slip/repair. I put half the bottle in the transmission and now it shifts like silk through every gear. I was amazed that half a bottle of liquid could make such a difference. I was just wondering if anyone else had a similar problem, or if anyone thinks that this is only a temporary fix??
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I am guessing that the final drive ratios for each version of the V8 will remain the same for 2007.
If so, that would mean that the overall first gear ratio in the six speed offers roughly 17.5% more torque multiplication than in the (now) ‘old’ five speed.
(Accounting in all numbers here for the roughly 2.33% diff. in rolling diameter between the STS-v’s 275 \ 40 x 19s and the STS’s optional 1SG \ QAF \ PCZ’s 255 \ 45 x 18s. I didn’t bother with looking at the 17” tires – this is left to the reader as an exercise – but I expect the result to be similar.)
In second gear there is a bit less than 7% more multiplication.
Third actually provides LESS multiplication – by over 4%. Odd.
Fourth offers roughly a 15% addition in multiplication.
Fifth offers roughly a 12% addition.
Sixth provides approx. 12% lower RPM at cruise.
Sounds interesting to me.
0 – 60 = 5.9 (R&T) and 6.0 (C+D)
Quarter = 14.3 @ 97.5 (R&T) and 14.6 @ 97 (C+D)
So.
My guess (does not rise to the level of a ‘fearless prediction’) is that even with no increase in HP or TQ, the 2007 V8’s standing start acceleration will be improved. Perhaps by as much as a half second in both 0 – 60 and the Quarter. Rolling acceleration ought to also be improved. I’m also guessing that seat-of-the-pants acceleration feel will be somewhat improved. ( Did I mention that I am an acceleration junkie? )
And the reduced sixth gear cruising RPM ought to provide somewhat better ‘real world’ highway fuel economy.
And this last is a (purely psychological) cool feature for me. I happen to like looking down at the tachometer and seeing a relatively low number while traveling at 70 – 80 mph. That’s just me. I have seen no evidence to suggest that today’s internal combustion engines cannot survive for a long time turning higher RPM. Certainly Infiniti, (for example) in warranting the powertrain in their M45s with ‘only’ a five speed trans, a fifth gear ratio of 0.83, and ‘only’ 27.8 MPH \ 1,000 RPM (vs roughly 36 MPH \ 1,000 RPM for the new & improved STS V8 with six speed) for 72 mo. or 70,000 miles.
But it is still a valid selling point – for me.
- Ray
Ready for my test drive . .
The primary advantage of cruising at a lower engine speed is that fuel consumption is reduced. My guess is that performance would be optimal with an axle ratio somewhere between 3.10 to 3.20 :1, but I don't know. I would guess that the 3.23:1 axle might be better than the 3.42:1 with the six speed. The overdrive ratio with the 3.23:1 axle would provide about the same overall ratio as the 2.73:1 and the 5 speed overdrive.
That’s actually something I was thinking about this weekend:
Will the magazines see enough different \ improved for 2007 to warrant publishing a(nother) test of the STS?
With the availability of a six speed (in place of the really old four speed) automatic on the 2006 Corvette being the only significant mechanical \ performance change compared to the 2005, it took over 6 months for any magazine to publish acceleration numbers. And (as far as I know) still no one has published a full test.
Unless there is a $60K – $65K Luxury Sedan Comparison test in the works, I doubt we’ll se a test of the 2007. The six speed and Brembo availability are just not enough different to justify re-test.
But I could be wrong.
- Ray
Likely depending on my finely calibrated ‘butt dyno’ during test drives to evaluate the 2007’s acceleration.
If the gears in the transmission were equally spaced, then the 5 speed gears would be 1.46 apart (0.75; 1.10; 1.60; 2.34; 3.42). The 6 speeds gears would be 1.43 apart (0.67; 0.96; 1.38; 1.97; 2.83; 4.06). The basic problem is that to choose each gear would require a planetary gearset for each one. The actual transmissions have only 3 planetary gearsets, so some gears can be choosen, and the rest are combinations. The 6 speed has its top gears closer together than the 5 speed. The interesting thing about the 5 speed is that third gear is half way between low and high. While the 6 speed gearing on average is closer together than the 5 speed's, it is not much closer together (1.46 vs 1.43). The 6 speed seems to provide a somewhat lower first gear and a higher overdrive, so that somewhat better performance and fuel economy can both be expected. The EPA numbers for the Corvette do not seem to be that much different however.
The 6 speed, with the wider ratio spread, does indeed provide the opportunity for both enhanced acceleration in first and second gear as well as reduced RPM and therefore better fuel economy in the higher gears at cruise.
The Corvette is an interesting case, in this respect.
The replacement of the four speed with the six speed resulted in a loss of one MPG city and the gain of one MPG highway. The change was accompanied by a switch to the 2.56:1 final drive ratio. With the A4, it was 2.73 with option of 3.15. The A4 ratio spread was 4.37. And the 2006 Corvette’s new six speed has identical internal ratios to the 2007 STS’s.
My take (after reading 2 sources) is that GM \ Chevy managed to deliver acceleration approx. equal to the C6 A4 with the 3.15 (G90 Performance ratio & sometimes on constraint) final drive while simultaneously achieving fuel mileage approx. equal to the C6 A4 with the 2.73 final drive.
There is now only 1 final drive ratio for the automatic Corvette.
Anyway – it appears that you and I are the only 2 posters on Edmunds that even care a little bit about any of the 2007 “stuff”. I guess that accounts for the last unsold inventory numbers I saw for 2006 STSs (well over 120 days) and the current apparent ability to buy one for well under invoice.
- Ray
Still ready for my 2007 test drive . .
I think that GM's choice of low gear ratios on their six speeds (both RWD and FWD) are perhaps a bit too low. On the other hand, other production six speed automatics are using quite low first gear ratios, so I am sure that there is a reason.
Thanx again for the info
2 - I have seen nothing to indicate significant upgrade(s) to the interior for 2007.
But we'll see - in a couple of months.
- Ray
Also waiting . .
Playing around with my spreadsheet and the equations for planetary gearsets suggest that one could get from two planetary gears the following six ratios (4:1, 2.8:1, 1.9:1, 1.33:1, 1:1, 0.75:1). This would have the top three gears a bit closer together than the bottom three. Compared to the 5 speed, this would have a lower first gear, so the axle ratio could be changed from 3.42 to 3.08. This would give a lower overall ratio in the first 5 gears and still provide an overdrive ratio that is more fuel efficent. A 2.73:1 axle ratio would be somewhat mixed, some lower, some higher.
I guess that my point is that I do not fully understand GM's choice of gears, or the sense in an overall ratio of the transmission to be 6:1. Based on the Covette's EPA results, I think the city mileage is not so good. The 2007 Saturn Aura is rated 18/27 with the 3.6 and six speed transmission, while the base Aura's 3.5 engine and 4 speed automatic are rated 20/30. This does not show that the six speed is resulting in better fuel economy. This may be a quirk in the EPA testing.
5L40-E tranny smooth as silk until 21K mi
shifting is now harsh in all shifts except 1-2
Any ideas ?